A Multi-Input Multi-Output (MIMO) scheme means that a base station and a user equipment simultaneously transmit several data streams (or layers) spatially by using two or more transmitting/receiving antennas so as to increase system capacity. The MIMO scheme includes a transmit diversity scheme, a spatial multiplexing scheme, or a beamforming scheme.
The transmit diversity scheme is advantageous in that same data information is transmitted through several transmitting antennas to implement data transmission of high reliability without channel feedback from a receiver. The beamforming scheme is used to increase a received signal to interference plus noise ratio (SINR) of a receiver by multiplying several transmitting antennas by proper weight values. Generally, since uplink/downlink channels are independent in a frequency division duplexing (FDD) system, channel information of high reliability is required to obtain proper beamforming gain. In this case, the channel information is separately fed back from the receiver.
Meanwhile, the spatial multiplexing scheme may be divided into a single user spatial multiplexing scheme and a multi-user spatial multiplexing scheme. The single user spatial multiplexing scheme is referred to as a spatial multiplexing (SM) scheme or a single user MIMO (SU-MIMO) scheme. In the single user spatial multiplexing scheme, a plurality of antenna resources of a base station are allocated to a single user (user equipment), and capacity of a MIMO channel is increased in proportion to the number of antennas. Meanwhile, the multi-user spatial multiplexing scheme is referred to as a spatial divisional multiple access (SDMA) scheme or a multi-user MIMO (MU-MIMO) scheme. In the multi-user spatial multiplexing scheme, a plurality of antenna resources of a base station or radio spatial resources are distributed to a plurality of users (user equipments).
Examples of the MIMO scheme include a Single CodeWord (SCW) scheme and a Multiple Code Word (MCW) scheme, wherein the SCW scheme is intended to transmit N number of data streams (or layers) at the same time by using single channel encoding block, and the MCW scheme is intended to transmit N number of data streams by using M (M≦N) number of channel encoding blocks. In this case, each channel encoding block generates independent codewords, each of which is designed to enable independent error detection.
Generally, in a communication system, a user equipment existing in the communication system may receive an interference signal from neighboring base stations that are adjacent to a service base station.
In particular, the user equipment located at the cell edge may be more affected by interference of base stations of a neighboring cell than the user equipments located at the cell interior. This interference signal is one of important factors that reduce transmission efficiency of a data rate of a transmitting signal.
Recently, in a multi-user interference channel environment where a plurality of base stations transmit data a plurality of user equipments while interfering with one another, a method for improving system capacity has actively studied.
Generally, in an actual environment, inter user interference between user equipments existing within the service base station as well as inter-cell interference generated by neighboring base stations occurs.
Accordingly, considering inter cell interference and inter user interference, studies on the interference control technology that may use restricted radio resources within the maximum range will be required.